OK335xS 系统启动配置解析

一、参考文档：
    AM335x ARM® Cortex™-A8 Microprocessors (MPUs) Technical Reference Manual

二、SYSBOOT Configuration Pins Notes(page 4111):
    1. WAIT is monitored on GPMC_WAIT0.
    2. MUX1 and MUX2 designate which group of XIP signals are used. Each group is defined in Table 26-9.
    3. Note that even though some bits may be a "don't care" for ROM code, all SYSBOOT values are latched into the CONTROL_STATUS register and may be used by software after ROM execution has completed.
    4. SYSBOOT[15:0] terminals are respectively LCD_DATA[15:0] inputs, latched on the rising edge of PWRONRSTn.
        LCD_DATA[15:0]引脚电平在PWRONRSTn上升沿的时候被锁定进入SYSBOOT[15:0]

三、Current Configuration:
    1. SYSBOOT[15:0]: 0b0100 0000 1000 0100
    2. 参考表格：Table 26-7. SYSBOOT Configuration Pins[4](page 4106)
    3. 分析配置：
        +--------+----------------+----------------+----------------+---------------+
        |  Bits  | SYSBOOT[15:14] | SYSBOOT[13:12] | SYSBOOT[11:10] | SYSBOOT[9]    | 
        +--------+----------------+----------------+----------------+---------------+
        |  value |     01         |       00       |      00        |      0        | 
        +--------+----------------+----------------+----------------+---------------+
        |  mode  |  01b = 24MHz   |    reserved    |non-muxed device|ECC done by ROM| 
        +--------+----------------+----------------+----------------+---------------+
        |  Bits  | SYSBOOT[8]     | SYSBOOT[7:6]   | SYSBOOT[5]     | SYSBOOT[4:0]  | 
        +--------+----------------+----------------+----------------+---------------+
        |  value |      0         |       10       |       0        |               | 
        +--------+----------------+----------------+----------------+               |
        |  mode  |  8-bit device  |   Don't care   |CLKOUT1 disabled|               | 
        +--------+----------------+----------------+----------------+               |
        |  Bits  |                 Boot Sequence                    |               | 
        +--------+--------------------------------------------------+               |
        |  value |                                                        00100     | 
        +--------+------------------------------------------------------------------+
        |  mode  |                 1.UART0 2.XIP 3.MMC0 4.NAND                      | 
        +--------+------------------------------------------------------------------+